Implantable prosthetic heart valves are typically formed of an annular mechanical valve seat in a valve body and one or more occluding disks or leaflets that are movable between a closed, seated position and an open position in a prescribed range of motion. Prosthetic mechanical heart valves may be formed of blood compatible, non-thrombogenic materials, typically comprising pyrolytic carbon and titanium with hinge mechanisms and/or pivoting guides prescribing the range of motion of the disk or leaflets. Prosthetic tissue valves are formed from treated integral swine valve leaflets and valve annulus structure mounted to an annular valve body.
Such prosthetic heart valves are commonly provided with a suturing ring surrounding the valve body that is sewed by the surgeon to the peripheral tissue of a natural heart valve orifice after surgical removal of damaged or diseased natural valve structure. The suturing ring and valve body are typically fabricated so that they may be rotated with respect to one another by the application of force. Following implantation, the surgeon may desire to adjust the valve leaflet or disk orientation by rotation of the valve body within the suturing ring so that the valve mechanism can properly operate without interference from the surrounding heart tissue. Adjustment by rotation of the valve body requires a rotational force sufficiently small as to avoid damage to the sutured heart tissue or loosening of the sutures, and yet sufficiently great so that the valve, when properly positioned, does not further rotate during its long term operation.
The outer fabric layer of the typical suturing ring of the type shown in U.S. Pat. Nos. 4,197,593, 4,790,843, and 5,178,633 is porous and tear resistant so that needles and sutures pass through it when the suturing ring is sutured in place. Clinical studies indicate that a type of fibrous tissue forms on the suturing ring fabric layer as a result of the initial deposition of thrombus and its subsequent organization into avascular, that is tissue without vascularization, fibrous tissue. Normally, this is not a clinical problem, and the thin layer tissue formation and shallow growth into the fabric weave interstices is viewed as a positive factor in the stabilization of the suturing ring. Sometimes, however, a thick, vascular fibrous tissue is evolved through granulation tissue and the growth of capillaries in it. This type of fibrous tissue not only extends into the interstices of suturing ring fabric but also covers the suturing ring, and may produce procoagulant activity. More significantly, this type of vascular fibrous tissue often becomes excessively thicken as it continues to grow over the margin of the suturing ring and intrudes into the valve's annular opening and interferes with the range of motion of the leaflets or disk. This excessive growth is referred to in the literature as "pannus" overgrowth.
A thin carbon film coating of Biolite.RTM. carbon coating has been applied on some certain heart valve suturing rings, e.g., on the suturing rings of the Omnicarbon.RTM. valve and the Bjork-Shiley.RTM. valve. This kind of coating does not create an impermeable or semi-impermeable surface and does not reduce the surface porosity of a suturing ring, but is claimed to increase biocompatibility. Tissue ingrowth into the Biolite.RTM. coated, fabric interstices is intended and occurs.
It is desirable that a suturing ring for an artificial heart valve be provided that inhibits or minimizes tissue ingrowth into the valve annular opening yet acts to stabilize the valve suturing ring.